Variability of the Kuroshio in the East China Sea derived from satellite altimetry data

Abstract

We investigate the spatial and temporal surface variability along the entire Kuroshio Current in the East China Sea (ECS) using 16-year (1993–2008) surface geostrophic currents derived from satellite altimetry data. Our analysis is based on stream coordinate and physically sensible definitions of the axis, width, along- and cross-stream transports. Mainly flowing along the 200 m isobath, the Kuroshio's width narrows from ∼218 km in the winter towards ∼207 km in the summer while the surface transport increases from a minimum of 6.8×10 4 m 2/s in the autumn to a maximum of 7.4×10 4 m 2/s in the summer. The width, surface transport, and the magnitude of the along-stream velocity of the Kuroshio are positively correlated along its track and have relatively large values in the central ECS. The shoreward intrusion that departs from the mainstream chiefly occurs near the southwest of Kyushu where an estimated transport of 1.8 Sv of the Kuroshio veers towards the Tsushima Strait throughout the year. The surface shoreward intrusion in other parts of the Kuroshio is generally weak and most of the transport that deviates shoreward from the core (around the 200 m isobath) of the Kuroshio recirculates within the stream. The net surface transport induced by Ekman process along the stream contributes to the surface shoreward intrusion, and the intrusion in the entire vertical water column is, nevertheless, controlled by the local geostrophic current. The spatial structure of the intrusion is mostly governed by the response of stream to shelf topography between the 200 m isobath and the shore-side boundary. The transport across the shore-side boundary of the Kuroshio is considerably different from the transport across the 200 m isobath, and the former better reflects the water exchange between the stream and the ECS shelf.